Hundreds of billions of stars. Tens of trillions of potentially colonizable worlds, supporting sextillions to septillions of humans researching the truths of the cosmos and the betterment of our lives. Humanity becoming immune to extinction by spreading itself out among the stars, and with the resources of a whole galaxy or more toward improving our quality of life. Scientific discoveries beyond imagination. This is the future that humans face should we ultimately take to the sky.
The problem is, our cave-dwelling ancestors were technologically closer to building modern Tokyo than we are to interstellar colonization. This diary series discusses how humanity might take its first baby steps in the direction of an interstellar future. Today we will focus on the question of, "Where do we start?"
This is the second diary in the "Colonization Of Other Worlds" series.
Part One: Beyond The Space Elevator: A Glimpse Of Alternative Methods For Space Launch
Part Two: Where Will We Begin?
To begin, we must first define terms. We are discussing the formation of a colony, as opposed to a base. A base is a location where people live which is entirely or nearly entirely dependent on another location for its survival and expansion. A colony is a location where people live which is largely or completely independent of other locations for its survival and expansion.
While building a base (such as the International Space Station) may make for nice footage and can help us conduct research into how to live off-world, it provides no benefits in terms of making ourselves less of a one-planet species. Hence, we shall focus on the daunting task of colonization.
We will assume that, as in our last diary, we have developed a means of high-throughput, low-cost access to space. While we currently struggle to reach a prices of a few thousand dollars per kilogram, to begin the arduous process of colonizing another world, we will need prices in the lower hundreds of dollars per kilogram or less to LEO and not dramatically more to the surface of other worlds. This is not a near-term capability, but all signs suggest that it is more than technically possible with current technology via one of many different possible routes if sufficient funds are invested.
The question then arises: which world should become our first colony -- if it should be on a world at all? We will discuss some of the more significant prospects in the inner solar system.
The Moon
Pros:
- Easy to transport goods to and from Earth.
- Very short communications and transit times, with extremely frequent launch windows.
- Low delta-V requirements for landing and departure.
- A (brief) previous history of manned exploration.
Neutral:
- Ice available, but subsurface and not well geographically distributed.
- 50% radiation shielding, due to the large mass of matter on one side of you.
Cons:
- Very poor surface mineral diversity and distribution. Most of the moon is exceedingly poor in volatile elements like carbon, hydrogen, oxygen, and nitrogen -- the essential elements of life and industry. It is also poor in heavy metals. The moon's poor geologic diversity is a result of the process of its formation and its long exposure to the solar system without an atmosphere.
- Two-week long days followed by two-week long nights. Few plants can tolerate such a growth cycle, so artificial lighting (and its associated energy requirements) are a requirement.
- Abrasive and likely dangerous electrostatic dust clings to everything and could potentially ruin the prospects of lunar telescopes, as well as increasing wear on all exposed machinery.
- The moon's shortage of heavy metals (which were largely lost to Earth during the collision) makes solar power the most likely sustainable energy source -- but the long day means exceedingly large energy storage requirements, except in very rare locations. Alternative exist, such as power beaming from space, but these carry their own risks and would involve a self-sustained lunar space program -- meaning reestablishing one of the most high-tech industries on Earth on the moon (albeit with easier launch requirements).
- 0.17 G raises concerns about potential health problems for people born and raised on the moon.
- The short distance raises questions about how immune to annihilation from conflicts on Earth such a lunar colony would be.
Space
Pros:
- Lacking a surface, it is easier to spin up to a full 1G for occupants' health.
- A colony built by mining out, say, the mass of Ceres alone would create hundreds of times more livable space than the entire land surface of Earth.
- No electrostatic dust.
- More mineral diversity (for example, the ability to mine volatiles from carbonaceous chondrites, various heavy metals without the requirement for deep mining, etc)
- The relatively common presence of minerals that are rare on Earth.
- Excellent solar power availability.
- Even lower delta-V requirements from Earth than for the Moon.
- Can custom-set the day length.
Cons:
- All of the advantages of a given location are not provided to all locations. For example, a colony near the sun has excellent power but poor resource availability, while a colony in the asteroid belt has excellent resource availability but little sunlight. A colony on an elliptical orbit between the two suffers from both problems.
- Serious radiation shielding requirements.
- Mining in microgravity, while benefitting from easy transportation of ores off the surface, is expected to be significantly more difficult than in a gravity well.
- While better than the moon, there are still major element distribution differences between asteroids and Earth that may be difficult to overcome in order to recreate our current tech base that colonists in space would be reliant on for their survival.
- Mining requires numerous bases scattered through space transferring a wide range of raw materials and finished products amongst them, unless the entire colony is to be moved around from orbit to orbit chasing ore after ore.
- In the very long-term picture, impossible to terraform (althoug,h ultimately, one could make extremely large areas that mimic outdoor space).
- Micrometeoroids and space debris.
Mars
Pros:
- Perhaps the most likely body in the solar system to bear a similar surface element distribution to Earth -- including huge amounts of water ice. This includes widespread subsurface ice, polar caps, and highland glaciers.
- The only large natural body in the solar system with a day length similar to Earth's.
- An atmosphere, however tenuous (0.007 ATM), allowing for aerobraking and aerocapture as well as providing moderate radiation shielding on top of that provided by the planet itself. Some additional minor radiation shielding is provided by a very weak magnetic field.
- A fair amount of robotic exploration has already been conducted and will be conducted before a colonization program ever gets underway.
- Aesthetically (and thus psychologically), the probably closest match to Earth outside the walls of the colony's buildings.
- In the very long-term picture, probably the easiest to terraform.
- A surprisingly geologically active planet with signs of modern volcanism, including a methane signature. Might geothermal power generation be possible in places?
- Massive caves.9) Dramatic annual geologic events, such as explosive ice cap geysers.
Neutral:
- 0.38G gravity's affects on human health is unknown.
- While delta-V requirements to get off the surface are much lower than on Earth, they're still higher than most other potential colonization targets.
- Weak dust devils -- these are more likely to be a benefit than a penalty, however, as they tend to clean the dust off surfaces.
- Frost in some regions -- adding weight to structures, but also providing a potential resource.
- Wind does occur, and with significant speed -- however, the atmosphere is too thin for it to make for a reasonable electricity generation source with current windpower technology.
- Like most colonization sites, it would be difficult if not impossible to adapt food crops to growing in the extreme temperature and near vacuum conditions outside. Greenhouses would be required.
Cons:
- Abrasive electrostatic dust (although of a different, and probably less hostile, nature than that found on the moon).
- Due to the earthlike mineral distribution, Mars is perhaps harder to make an economic argument for its colonization -- although due to the extremely long payback times, it's hard to make an private capital argument for any sort of colonization program (more on this and ways around it in the next diary in this series).
- Planetwide dust storms require a means of backup power generation or significant energy storage if solar power is the source.
- One of the lowest solar power availabilities of likely colonization locations.
Mercury
Pros:
- The highest solar-power availability on the surface of a large body in the solar system. Mercury's solar constant ranges from 4.6x to 10.6x that on Earth.
- Extremely metal-rich as a whole (although what is available at the surface is still largely unknown). This combines with #1 to suggest that Mercury might ultimately make an excellent mining world.
- Anticipated to be geologically active, due to the presence of a significant magnetic field. Geologic activity increases mineral prospects and the prospect of geothermal electricity generation.
Neutral:
- The surface gravity is the same as that on Mars (0.38G)
- Has an "exosphere" (extremely thin atmosphere) of hydrogen, helium, oxygen, sodium, calcium, potassium, and other volatile elements. How this will benefit or hinder human activities on the planet is unknown.
- Ice available, but subsurface and not well geographically distributed.
- Has a small magnetic field which provides some radiation shielding, but lacks an atmosphere and is close to the sun, increasing the surface flux.
Cons:
- Expected to be very depleted in volatiles -- worse than the moon.
- The solar flux may be too overwhelming; colonies will need to be very reflective and insulated, with good radiative cooling systems.
- A long 59-day rotation, not tidally-locked with the sun, means that significant power must be stored up during the day or a means of backup power generation be available. No "peaks of eternal light" are yet known on Mercury.
- Experiences a complicated interplay between the solar wind and surface exposure to solar radiation, which changes dynamically. The surface undergoes "space weathering" when low energy solar plasma impacts it.
The cloud tops of Venus
Pros:
- Perhaps the most Earthlike place in our solar system outside of Earth. At 53km, the pressure is just under 0.6 ATM (the pressure in La Paz, the capital of Bolivia) and the temperature averages just over 30C (Phoenix in the middle of the day during May).
- Gravity of just under 0.9g at the cloudtops -- very similar to that on Earth.
- While Venus's day is a staggering 243 Earth days, the cloud tops undergo "superrotation", rotating the planet every four Earth days.
- The atmosphere itself provides significant quantities of carbon, oxygen, nitrogen, and sulfur, as well as small amounts of deuterium-enriched water.
- A metal-rich surface with extensive volcanism, including 167 volcanoes of the scale of the Hawaiian system. Observed surface lightning and thunder, as well as SO2 changes, are considered potential signs of ongoing volcanism.
- Possible metallic "snow", believed to be anything from the thin-film solar cell material tellurium to lead and bismuth sulfides, has been observed on Venusian mountaintops.
- Common crops could possibly be able to be engineered to grow exposed to the extreme conditions of the venusian atmosphere. Bacteria are known to grow in conditions far more extreme than that.
- More frequent launch windows than Mercury or Mars and an excellent atmosphere for aerocapture.
Neutral:
- Venus has a negligible magnetic field. Only the atmosphere above the colony would provide more shielding than a bare exposed rock in the same orbit would experience.
- Requires a floating colony, which one would expect to be a significantly more difficult construction task than a surface colony. However, the atmosphere is denser for the same pressure, and hydrogen won't burn, so the buoyancy requirements aren't as bad as they could be otherwise. One interesting possibility is that air with a composition similar to earth's atmosphere is a lifting gas on Venus -- hence transparent-roofed blimps with colonized interiors could provide both buoyancy and earthlike habitable space.
Cons:
- The surface of the planet is practically inaccessible, with pressures of 93 ATM and equatorial temperatures of nearly 500C (hot enough to melt lead). If the surface cannot be mined, then mining would have to be done off-planet, meaning significant delta-V. This would make Venus's cloud tops more like a base than a planet.
- 53km is in the middle of Venus's cloudtops, which are comprised of sulfuric acid droplets floating in what is primarily carbon dioxide. Concerning stepping outside: While carbon dioxide is not an irritant to the skin and the sulfuric acid is sparse, the acid will likely prove an irritant, requiring either gas scrubbing systems around open areas or protective clothing when outdoors. Eye protection would be required even if the SO2 was scrubbed due to the toxic effect of high concentrations of CO2 to the eyes. An oxygen supply would be required for breathing. The risks of chronic skin exposure to the low levels of carbon monoxide (~17ppm) on Venus would have to be assessed. Pressure suits would not be needed.
- Venus's clouds above the colony would reduce the insolation at the colony -- although the planet is closer to the sun than Earth, partially compensating for this fact.
- There may be a lightning risk due to cosmic radiation discharges. Venus has been confirmed to experience lightning in amounts comparable to that on Earth.
- The Soviet Vega probes, which each deployed a balloon at 53km altitude, found that there can be powerful convection cells at times.
Overview:
Each potential colonization site bears its own strengths and weaknesses. Some, like Mercury and Venus, have both tremendous potential strengths and tremendous potential weaknesses. Others, like Mars, are more balanced.
One means of potentially addressing the day/night power generation issue on some of bodies could be geothermal heat storage. Especially on bodies lacking an atmosphere, the surface temperature will fluctuate wildly depending on whether it is exposed to light or not while the deep subsurface will remain relatively constant in terms of temperature. This temperature differential can allow for electricity generation -- although the economics of such a proposal are unknown.
A key focus in site selection will be the ability to effectively grow food. Water can be recycled with small losses and found in most places, while oxygen is incredibly abundant in many forms in the solar system. But two other things are required to grow food: nutrients and light.
Life requires a suitable source of CHONP: Carbon, Hydrogen, Oxygen, Nitrogen, and Phosphorus. Higher organisms require sizeable quantities of sodium, magnesium, sulfur, chlorine, potassium, and calcium, and trace amounts of manganese, iron, cobalt, nickel, copper, zinc, selenium, molybdenum, and iodine. Many of these elements are volatile and may be hard to come by on bodies that are not protected by an atmosphere and/or magnetic field. Even if sites are found on other bodies to mine them, they may only be found in low quantities and/or require significant transportation of raw materials from many different locations back to the colony.
Light can be provided by sunlight (which varies dramatically between different sites) or artificial lighting. If the day length is longer than a few Earth days, artificial lighting will almost certainly be required. While artificial lighting may seem a ready solution, manufacture of efficient sources of artificial light, such as LEDs, requires an advanced technology base, and even LEDs require huge amounts of power (which may be difficult to produce from the very limited local industry) per the amount of food grown.
Of the bodies analyzed, Mars seems to be the best rounded site for initial colonization, followed by space colonies once technology is developed enough to allow for significant interplanetary trade. Mercury and Venus seem to offer interesting mining possibilities, with Mercury combining that with excellent energy resources and Venus's possible outdoor farming -- but both have huge challenges associated with them that make them poor candidates for initial colonization. The moon has the benefit of convenience, but not much else going for it.
It is worth noting that there may be targets in the outer solar system of interest in the future. The outer solar system poses a number of challenges -- intense radiation belts at the gas giants, smaller solid bodies, greatly reduced solar radiation, much greater transit times, and so forth. For future diaries in this series, we will assume the colonization of Mars. In our next diary, we will examine who is likely to first organize and fund the colonization of the planet, the economics of it, and what sort of political systems we might encounter.